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Published on: 5/6/2025

What Causes Knee Pain When Bending and Straightening the Leg?

Knee pain when bending and straightening can be caused by problems with the tissues around the knee such as the cartilage, tendons, or muscles. It may also be due to conditions like arthritis or issues with the way the kneecap moves.

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Explanation

When you bend or straighten your knee, many parts have to work together. Sometimes, the pain happens because the cartilage that cushions your joint is worn away, as seen in arthritis. This makes the surfaces of your knee rub together, causing pain. The tendons that connect your muscles to your knee, like the quadriceps or patellar tendon, can also become irritated or inflamed (a condition called tendonitis). Another common cause is an issue with how the patella, or kneecap, moves within its track. If it doesn’t move smoothly, it can rub against the bone and hurt. In some cases, there might be injury to the knee’s soft tissues from overuse or a sudden twist, leading to strains or small tears in the ligaments or tendons. These problems are described in medical reviews, and doctors carefully check to see which one matches the symptoms. Understanding the cause of the knee pain helps in guiding the best treatment and exercises for healing and strengthening the knee.

(References)

  • Duong V, Oo WM, Ding C, Culvenor AG, Hunter DJ. Evaluation and Treatment of Knee Pain: A Review. JAMA. 2023 Oct 24;330(16):1568-1580. doi: 10.1001/jama.2023.19675. PMID: 37874571.

  • Kuwabara A, Fredericson M. Narrative: Review of Anterior Knee Pain Differential Diagnosis (Other than Patellofemoral Pain). Curr Rev Musculoskelet Med. 2021 Jun;14(3):232-238. doi: 10.1007/s12178-021-09704-9. Epub 2021 Apr 5. PMID: 33818700; PMCID: PMC8137785.

  • Petersen W, Rembitzki IV, Brüggemann GP, Ellermann A, Best R, Koppenburg AG, Liebau C. Anterior knee pain after total knee arthroplasty: a narrative review. Int Orthop. 2014 Feb;38(2):319-28. doi: 10.1007/s00264-013-2081-4. Epub 2013 Sep 22. PMID: 24057656; PMCID: PMC3923935.

  • Updated 2023 Apr 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: [https://www.ncbi.nlm.nih.gov/books/NBK554587/

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